Wingman703

Issue: Misfire above 5500K RPM.
Setup: LS coils(Rockauto generics) wired to MS in batch fire, NGK Miata plug wires "crimped" to fit the LS coils, NGK BKR7E's gapped to .20", BP4W head shaved .008", VVT bottom end(12:1 compression).
This ignition setup should be bulletproof for my power levels(~160WHP) but from ~5500-7500RPM I have a misfire I believe is ignition related. I can feel the misfire "kick in" and the log shows rich dips along with slight losses of RPM.
Spark plugs show strong spark when operating in test mode all the way to 20K RPM(batch fire, so they should only be seeing ~15K at redline).
Misfire does not appear at any other RPM ranges or load conditions.

Possible ideas:
One or more coils is "bad" and only shows up at greater than 5500RPM under load
The Miata plug wires aren't sufficient when "adapted" to the LS coils and they are intermittently fizzing out during pulls
Coils are overheating and cutting out due to being used at twice their intended RPM(LS's see what... 6500RPM?)

Anyone have other suggestions before I throw $400 in new OEM coils/ custom Magnacore wires at it? I'm running MS2 so rewiring the coils for sequential spark is impossible at this point due to all drivers being used.
Tune and log attached.

patsmx5

iTrader: (16)

I'm assuming 0.020" not 0.2".

What dwell? I would try the iridium plugs, the tiny iridium tip is easier to fire at the same gap than a basic copper plug.

But the stock coils can run 0.040" gap on a NA motor, so something is definitely wrong.

Wingman703

Err, yes on the gap. .020". FWIW I felt no change in the misfires when I gapped them down from whatever they come stock with, .05" I'd guess?
4.5 dwell, 1.5ms spark duration. Below is my entire ignition options page.
Are the BKR7E's not iridium tips? I saw them as the step colder all the turbo guys go to. While I double I have the same cylinder pressure as a boosted motor I'm sure I have a good bit more than a stock engine due to the static compression increase.

SpartanSV

BKR7E is a regular copper plug. I run the iridium version in the 8 heat range at 235kpa+ on stock NA8 coils. BKR8EIX is the part number.

Your log is interesting. It does have a rich area I can't explain, but your theory on it being from a misfire is incorrect. Oxygen sensors read oxygen not fuel. A misfire leads to excess oxygen in the exhaust. The oxygen sensor has no idea the engine misfired so its thinking all that extra oxygen was caused by a very lean fuel mixture. Misfires will always register as lean on an oxygen sensor.

Wingman703

I'm only running stock NB1 injectors but I highly doubt I'm running out of fuel in that manner, especially since I can pull 10:1 AFR if I dump tons of fuel into the VE table.
I'll swap for iridium plugs and magacore wires and see if that makes any difference since that's much cheaper then new coils. Would you suggest sticking to 7's or moving to 8's for heat range?

SpartanSV

I would run 7's at your HP level. It really didn't look like a spark blowout issue to me and I'd expect your current plugs to be fine for your setup.

I really think your issue is elsewhere. How easily could you monitor fuel pressure? I had a fuel pump connector failure that caused similar symptoms and logs.

Wingman703

I'd have to rent a tester and monitor it manually through the windshield. Not impossible, but a bit more tricky then just popping new plugs/wires in.
If said plugs/wires have no effect I'll look into fueling issues. Expect to hear more within a week or two.

Wingman703

Update: no closer to finding the issue.
I've swapped in a fresh set of BKR7EIX's, gapped to .02
Ordered a custom set of leads from Magacore, 8.5mm reds with Miata spark ends and LS coil ends.
Issue still persisted. I had two extra coils in my spare parts bin, so I swapped them out for each of the current coils. No change.
Rented a fuel pressure tester, fuel pressure looks golden to me. 40PSI when primed, 34-35PSI at idle, 42-44PSI holding firm at WOT.

At this point, what else could it be? A failing injector? They are all stock NB1 injectors from various origins(i.e, not all from the same car).
And FWIW, any rubber in the fuel system is fairly new(less than a year old) and fuel filter was changed inside the last 6 months.

Fuel test run, all of 3rd with some of 4th:

Picture of the engine bay for... reasons, idk, perhaps someone can point out something obvious I've missed.

curly

iTrader: (25)

Have you tried a new cam sensor?

gooflophaze

No sync losses, but a 12% timing error in the logs at the rich dip - so definitely a misfire. Dwell and duty cycle stable at time of misfire.

This is gonna sound backwards - but drop your dwell time to 4ms. There's some indications of some d585's auto triggering.

https://forums.holley.com/showthread...-Spark-Blowout

Wingman703

Issue happens with both my primary and backup cam/crank sensors. I'm not experiencing any sync loss.
Stock NB1 Cam sensor/cam gear, Stock NB1 Crank sensor with FM 36-2 trigger wheel.
Will try. Never heard of auto triggering before.
Learn me though, where did you find the "12% timing error"? That sounds like an important bit of troubleshooting knowledge.

gooflophaze

timing is 0.4 off prior to this "blip" and returns to 0.4ish afterwards. Timing error is basically the expectation of the next tooth vs when the next tooth is actually read.

Wingman703

goof, its my regret I can only give you one cat. This issue has been plaguing me for months and you solved it with two clicks.

Dropping the dwell to 4ms removed 95% of the misfires. I had a steady unbroken pull all the way to 7K where I had just one slight hiccup. Even let the car idle 10min to fully heat soak, then successfully repeated it twice. Unfortunately I neglected to bring my laptop so I couldn't drop the dwell any farther to see if that would clear up the very last remnants of the misfire. I've burned all my local pull spots and we have rain moving in heavy for the next week so that's where I'm going to have to leave it for now.

Should I continue to drop the dwell till it pulls smoothly to 7500RPM, or is this something that should be solved for in the "Dwell Battery Correction" table? My voltage holds near 12.8-13.1v from idle to redline.

gooflophaze

Eh, I'm just surprised it worked. I have some d585's from the junkyard to put in my brothers car once his built engine is ready to go in and remembered reading about some of them auto triggering.

gooflophaze

https://www.miataturbo.net/diy-turbo...d-82744/page9/

Savington has a dwell table in there, 3.5-ish. Also complaints about knock off d585's. But a good read.